The purpose of this study is to determine the phenotype of multiple extracellular matrix molecules in adult mouse glomeruli from different strains of mice. Our postulate is that mice prone to develop glomerulosclerosis have a higher level of expression of genes coding for extracellular matrix at baseline prior to the appearance of lesions. We used the increased sensitivity afforded by the polymerase-chain reaction to assess alpha-1 type I and several alpha chains of type IV collagen mRNA as well as laminin subchains and tenascin in freshly microdissected normal adult mouse glomeruli. RT-PCR reactions for mRNA encoding these components were also performed using mesangial cell lines previously isolated from the same strain of mice. Type IV collagen mRNA was easily detectable in normal adult mouse glomeruli as well as in the cell lines. On the other hand, type I collagen mRNA was not detected in normal glomeruli, despite increasing the number of PCR cycles from 25-45 (roughly a 1000 fold increase in sensitivity). Assays using competitive PCR were developed. The current study provides evidence that the expression of types I and IV collagen in normal glomeruli is regulated at the pretranslational level in vivo. They also provide evidence for a continuous turnover of basement membrane in the adult glomeruli. We have applied this method to a mouse strain which develops spontaneous glomerulosclerosis, the ROP-OS mouse. This mouse is originally derived from a radiation-induced mutation. Our preliminary data indicate that the mutation induces a rapid glomerulosclerosis on a ROP background but has little effect on a C a C57B background. The ROP-OS mouse has a 3 fold increase in mRNAs coding for type IV collagens and laminin early in life at a time when morphologic evidence of glomerulosclerosis is quite discrete.